Pump action refill ink jet printing mechanism

ABSTRACT

This patent describes an ink jet printer based around ink jet nozzles which utilize a pump action so as to rapidly refill a nozzle chamber for ejection of subsequent ink drops. The nozzle chamber includes a first actuator for ejecting ink and a second actuator for pumping ink into the nozzle chamber. The actuators can comprise thermal bend actuators having a conductive heater element encased within a material having a high co-efficient of thermal expansion. The heater element is of a serpentine form and is concertinaed upon heating.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their U.S. patent application serial numbers (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

Cross-Referenced US Patent Application Australian (Claiming Right of Priority from Docket Provisional Patent No. Australian Provisional Application) No. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART2O PO8019 09/112,744 ART21 PO7980 09/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399 09/112,791 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PP0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 09/113,111 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJMI5 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045 09/113,089 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 09/112,745 IR20 PP0881 09/113,092 IR21 PO8006 09/113,100 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010 09/113,064 MEMS05 PO8011 09/113,082 MEMS06 PO7947 09/113,081 MEMS07 PO7944 09/113,080 MEMS09 PO7946 09/113,079 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to ink jet printing and in particular discloses a Pump Action Refill Ink Jet Printer.

The present invention further relates to the field of drop on demand ink jet printing.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.

In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.

Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. The utilisation of a continuous stream ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilised by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)

Piezo-electric ink jet printers are also one form of commonly utilized ink jet printing device. Piezo-electric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilises a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezo electric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezo-electric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a Piezo electric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4584590 which discloses a sheer mode type of piezo-electric transducer element.

Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative form of ink jet printing based around ink jet nozzles which utilize a pump action so as to rapidly refill a nozzle chamber for ejection of subsequent ink drops.

In accordance with a first aspect of the present invention, there is provided an inkjet nozzle chamber having an ink ejection port in one wall of the chamber and an ink supply source interconnected to the chamber. The inkjet nozzle chamber can comprise two actuators the first actuator for ejecting ink from the ink ejection port and a second actuator for pumping ink into the chamber from the ink supply source after the first actuator has caused the ejection of ink from the nozzle chamber. The actuators can utilize thermal bending caused by a conductive heater element encased within a material having a high coefficient of thermal expansion whereby the actuators operate by means of electrical heating by the heater elements. The heater elements can be of serpentine form and concertinaed upon heating so as to allow substantially unhindered expansion of said actuation material during heating. The first actuator is arranged substantially opposite the ink ejection port and both actuators form segments of the nozzle chamber wall opposite the ink ejection port and between the nozzle chamber and the ink supply source. The method for driving the actuators for the ejection of ink from the ink ejection port comprises utilizing the first actuator to eject ink from the ejection port and utilizing the second actuator to pump ink towards the ink ejection port so as to rapidly refill the nozzle chamber around the area of the ink ejection port. The method for driving the actuators can comprise the following steps:

(a) activating the first actuator to eject ink from the ink ejection port;

(b) deactivating the first actuator so as to cause a portion of the ejected ink to break off from a main body of ink within the nozzle chamber;

(c) activation of the second actuator to pump ink towards the ink ejection port so as to rapidly refill the nozzle chamber around the area of the ink ejection port;

(d) activating the first actuator to eject ink from the ink ejection port while simultaneously deactivating the second actuator so as to return to its quiescent position; or otherwise

(e) deactivating the second actuator to return to its quiescent position.

The material of the two actuators having a high coefficient of thermal expansion can comprise substantially polytetrafluoroethylene and the surface of the actuators are treated to make them hydrophilic. Preferably, the heater material embedded in the thermal actuators comprises substantially copper. Further, the actuators are formed by utilization of a sacrificial material layer which is etched away to release the actuators. The inkjet nozzle chamber can be formed from crystallographic etching of a silicon substrate. Further, the thermal actuators are attached to a substrate at one end and the heating of the actuators is primarily near the attached end of the devices. The inkjet nozzle is preferably constructed via fabrication from a silicon wafer utilizing semiconductor fabrication techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings which:

FIG. 1 is a cross-sectional schematic diagram of the inkjet nozzle chamber in its quiescent state;

FIG. 2 is a cross-sectional schematic diagram of the inkject nozzle chamber during activation of the first actuator to eject ink;

FIG. 3 is a cross-sectional schematic diagram of the inkjet nozzle chamber after deactivation of the first actuator;

FIG. 4 is a cross-sectional schematic diagram of the inkjet nozzle chamber during activation of the second actuator to refill the chamber;

FIG. 5 is a cross-sectional schematic diagram of the inkjet nozzle chamber after deactivation of the actuator to refill the chamber;

FIG. 6 is a cross-sectional schematic diagram of the inkjet nozzle chamber during simultaneous activation of the ejection actuator whilst deactivation of the pump actuator;

FIG. 7 is a top view cross-sectional diagram of the inkjet nozzle chamber; and

FIG. 8 is an exploded perspective view illustrating the construction of the inkjet nozzle chamber in accordance with the preferred embodiment.

FIG. 9 provides a legend of the materials indicated in FIGS. 10 to 22; and

FIG. 10 to FIG. 22 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, each nozzle chamber having a nozzle ejection portal further includes two thermal actuators. The first thermal actuator is utilized for the ejection of ink from the nozzle chamber while a second thermal actuator is utilized for pumping ink into the nozzle chamber for rapid ejection of subsequent drops.

Normally, ink chamber refill is a result of surface tension effects of drawing ink into a nozzle chamber. In the preferred embodiment, the nozzle chamber refill is assisted by an actuator which pumps ink into the nozzle chamber so as to allow for a rapid refill of the chamber and therefore a more rapid operation of the nozzle chamber in ejecting ink drops.

Turning to FIGS. 1-6 which represent various schematic cross sectional views of the operation of a single nozzle chamber, the operation of the preferred embodiment will now be discussed. In FIG. 1, a single nozzle chamber is schematically illustrated in section. The nozzle arrangement 10 includes a nozzle chamber 11 filled with ink and a nozzle ink ejection port 12 having an ink meniscus 13 in a quiescent position. The nozzle chamber 11 is interconnected to an ink reservoir 15 for the supply of ink to the nozzle chamber. Two paddle-type thermal actuators 16, 17 are provided for the control of the ejection of ink from nozzle port 12 and the refilling of chamber 11. Both of the thermal actuators 16, 17 are controlled by means of passing an electrical current through a resistor so as to actuate the actuator. The structure of the thermal actuators 16, 17 will be discussed further herein after. The arrangement of FIG. 1 illustrates the nozzle arrangement when it is in its quiescent or idle position.

When it is desired to eject a drop of ink via the port 12, the actuator 16 is activated, as shown in FIG. 2. The activation of activator 16 results in it bending downwards forcing the ink within the nozzle chamber out of the port 12, thereby resulting in a rapid growth of the ink meniscus 13. Further, ink flows into the nozzle chamber 11 as indicated by arrow 19.

The main actuator 16 is then retracted as illustrated in FIG. 3, which results in a collapse of the ink meniscus so as to form ink drop 20. The ink drop 20 eventually breaks off from the main body of ink within the nozzle chamber 11.

Next, as illustrated in FIG. 4, the actuator 17 is activated so as to cause rapid refill in the area around the nozzle portal 12. The refill comes generally from ink flows 21, 22.

Next, two alternative procedures are utilized depending on whether the nozzle chamber is to be fired in a next ink ejection cycle or whether no drop is to be fired. The case where no drop is to be fired is illustrated in FIG. 5 and basically comprises the return of actuator 17 to its quiescent position with the nozzle port area refilling by means of surface tension effects drawing ink into the nozzle chamber 11.

Where it is desired to fire another drop in the next ink drop ejection cycle, the actuator 16 is activated simultaneously which is illustrated in FIG. 6 with the return of the actuator 17 to its quiescent position. This results in more rapid refilling of the nozzle chamber 11 in addition to simultaneous drop ejection from the ejection nozzle 12.

Hence, it can be seen that the arrangement as illustrated in FIGS. 1 to 6 results in a rapid refilling of the nozzle chamber 11 and therefore the more rapid cycling of ejecting drops from the nozzle chamber 11. This leads to higher speed and improved operation of the preferred embodiment.

Turning now to FIG. 7, there is a illustrated a sectional perspective view of a single nozzle arrangement 10 of the preferred embodiment. The preferred embodiment can be constructed on a silicon wafer with a large number of nozzles 10 being constructed at any one time. The nozzle chambers can be constructed through back etching a silicon wafer to a boron doped epitaxial layer 30 using the boron doping as an etchant stop. The boron doped layer is then further etched utilising the relevant masks to form the nozzle port 12 and nozzle rim 31. The nozzle chamber proper is formed from a crystallographic etch of the portion of the silicon wafer 32. The silicon wafer can include a two level metal standard CMOS layer 33 which includes the interconnect and drive circuitry for the actuator devices. The CMOS layer 33 is interconnected to the actuators via appropriate vias. On top of the CMOS layer 33 is placed a nitride layer 34. The nitride layer is provided to passivate the lower CMOS layer 33 from any sacrificial etchant which is utilized to etch sacrificial material in construction of the actuators 16, 17. The actuators 16, 17 can be constructed by filling the nozzle chamber 11 with a sacrificial material, such as sacrificial glass and depositing the actuator layers utilizing standard micro-electro-mechanical systems (MEMS) processing techniques.

On top of the nitride layer 34 is deposited a first PTFE layer 35 followed by a copper layer 36 and a second PTFE layer 37. These layers are utilised with appropriate masks so as to form the actuators 16, 17. The copper layer 36 is formed near the top surface of the corresponding actuators and is in a serpentine shape. Upon passing a current through the copper layer 36, the copper layer is heated. The copper layer 36 is encased in the PTFE layers 35, 37. Plan has a much greater coefficient of thermal expansion than copper (770×10−6) and hence is caused to expand more rapidly than the copper layer 36, such that, upon heating, the copper serpentine shaped layer 36 expands via concertinaing at the same rate as the surrounding teflon layers. Further, the copper layer 36 is formed near the top of each actuator and hence, upon heating of the copper element, the lower PTFE layer 35 remains cooler than the upper PTFE layer 37. This results in a bending of the actuator so as to achieve its actuation effects. The copper layer 36 is interconnected to the lower CMOS layer 34 by means of vias eg 39. Further, the PTFE layers 35/37, which are normally hydrophobic, undergo treatment so as to be hydrophilic. Many suitable treatments exist such as plasma damaging in an ammonia atmosphere. In addition, other materials having considerable properties can be utilized.

Turning to FIG. 8, there is illustrated an exploded perspective of the various layers of an ink jet nozzle 10 as constructed in accordance with a single nozzle arrangement 10 of the preferred embodiment. The layers include the lower boron layer 30, the silicon and anisotropically etched layer 32, CMOS glass layer 33, nitride passivation layer 34, copper heater layer 36 and PTFE layers 35/37, which are illustrated in one layer but formed with an upper and lower teflon layer embedding copper layer 36.

One form of detailed manufacturing process which can be used to fabricate monolithic ink jet print heads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

1. Using a double sided polished wafer 50 deposit 3 microns of epitaxial silicon heavily doped with boron 30.

2. Deposit 10 microns of epitaxial silicon 32, either p-type or n-type, depending upon the CMOS process used.

3. Complete a 0.5 micron, one poly, 2 metal CMOS process. The metal layers are copper instead of aluminum, due to high current densities and subsequent high temperature processing. This step is shown in FIG. 10. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 9 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

4. Etch the CMOS oxide layers down to silicon or second level metal using Mask 1. This mask defines the nozzle cavity and the bend actuator electrode contact vias 39. This step is shown in FIG. 11.

5. Crystallographically etch the exposed silicon using KOH. This etch stops on (111) crystallographic planes 51, and on the boron doped silicon buried layer. This step is shown in FIG. 12.

6. Deposit 0.5 microns of low stress PECVD silicon nitride 34 (Si3N4). The nitride acts as an ion diffusion barrier. This step is shown in FIG. 13.

7. Deposit a thick sacrificial layer 52 (e.g. low stress glass), filling the nozzle cavity. Planarize the sacrificial layer down to the nitride surface. This step is shown in FIG. 14.

8. Deposit 1.5 microns of polytetrafluoroethylene 35 (PTFE).

9. Etch the PTFE using Mask 2. This mask defines the contact vias 39 for the heater electrodes.

10. Using the same mask, etch down through the nitride and CMOS oxide layers to second level metal. This step is shown in FIG. 15.

11. Deposit and pattern 0.5 microns of gold 53 using a lift-off process using Mask 3. This mask defines the heater pattern. This step is shown in FIG. 16.

12. Deposit 0.5 microns of PTFE 37.

13. Etch both layers of PTFE down to sacrificial glass using Mask 4. This mask defines the gap 54 at the edges of the main actuator paddle and the refill actuator paddle. This step is shown in FIG. 17.

14. Mount the wafer on a glass blank 55 and back-etch the wafer using KOH, with no mask. This etch thins the wafer and stops at the buried boron doped silicon layer. This step is shown in FIG. 18.

15. Plasma back-etch the boron doped silicon layer to a depth of 1 micron using Mask 5. This mask defines the nozzle rim 31. This step is shown in FIG. 19.

16. Plasma back-etch through the boron doped layer using Mask 6. This mask defines the nozzle 12, and the edge of the chips.

17. Plasma back-etch nitride up to the glass sacrificial layer through the holes in the boron doped silicon layer. At this stage, the chips are separate, but are still mounted on the glass blank. This step is shown in FIG. 20.

18. Strip the adhesive layer to detach the chips from the glass blank.

19. Etch the sacrificial glass layer in buffered BF. This step is shown in FIG. 21.

20. Mount the print heads in their packaging, which may be a molded plastic former incorporating ink channels which supply different colors of ink to the appropriate regions of the front surface of the wafer.

21. Connect the print heads to their interconnect systems.

22. Hydrophobize the front surface of the print heads.

23. Fill the completed print heads with ink 56 and test them. A filled nozzle is shown in FIG. 22.

The presently disclosed ink jet printing technology is potentially suited to a wide range of printing systems including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers, high speed pagewidth printers, notebook computers with in-built pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic ‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trade mark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the preferred embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.

For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

The present invention is useful in the field of digital printing, in particular, ink jet printing.

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to UI45 above which matches the docket numbers in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

Actuator mechanism (applied only to selected ink drops) Description Advantages Disadvantages Examples Thermal An electrothermal Large force High power Canon Bubblejet bubble heater heats the generated Ink carrier limited 1979 Endo et al ink to above Simple to water GB patent boiling point, construction Low efficiency 2,007,162 transferring No moving parts High temperatures Xerox heater-in-pit significant heat to Fast operation required 1990 Hawkins et the aqueous ink. A Small chip area High mechanical al U.S. Pat. No. 4,899,181 bubble nucleates required for stress Hewlett-Packard and quickly forms, actuator Unusual materials TIJ 1982 Vaught expelling the ink. required et al U.S. Pat. No. The efficiency of Large drive 4,490,728 the process is low, transistors with typically less Cavitation causes than 0.05% of the actuator failure electrical energy Kogation reduces being transformed bubble formation into kinetic energy Large print heads of the drop. are difficult to fabricate Piezo- A piezoelectric Low power Very large area Kyser et al U.S. Pat. No. electric crystal such as consumption required for 3,946,398 lead lanthanum Many ink types actuator Zoltan U.S. Pat. No. zirconate (PZT) is can be used Difficult to 3,683,212 electrically Fast operation integrate with 1973 Stemme U.S. Pat. No. activated, and High efficiency electronics 3,747,120 either expands, High voltage drive Epson Stylus shears, or bends to transistors required Tektronix apply pressure to Full pagewidth IJ04 the ink, ejecting print heads drops. impractical due to actuator size Requires electrical poling in high field strengths during manufacture Electro- An electric field is Low power Low maximum Seiko Epson, Usui strictive used to activate consumption strain (approx. et all JP 253401/96 electrostriction in Many ink types 0.01%) IJ04 relaxor materials can be used Large area such as lead Low thermal required for lanthanum expansion actuator due to low zirconate titanate Electric field strain (PLZT) or lead strength required Response speed is magnesium (approx. 3.5 marginal (˜10 μs) niobate (PMN). V/μm) can be High voltage drive generated without transistors required difficulty Full pagewidth Does not require print heads electrical poling impractical due to actuator size Ferro- An electric field is Low power Difficult to IJ04 electric used to induce a consumption integrate with phase transition Many ink types electronics between the can be used Unusual materials antiferroelectric Fast operation such as PLZSnT (AFE) and (<1 μs) are required ferroelectric (FE) Relatively high Actuators require a phase. Perovskite longitudinal strain large area materials such as High efficiency tin modified lead Electric field lanthanum strength of around zirconate titanate 3 V/μm can be (PLZSnT) exhibit readily provided large strains of up to 1% associated with the AFE to FE phase transition. Electro- Conductive plates Low power Difficult to operate IJ02, IJ04 static are separated by a consumption electrostatic plates compressible or Many ink types devices in an fluid dielectric can be used aqueous (usually air). Upon Fast operation environment application of a The electrostatic voltage, the plates actuator will attract each other normally need to and displace ink, be separated from causing drop the ink ejection. The Very large area conductive plates required to achieve may be in a comb high forces or honeycomb High voltage drive structure, or transistors may be stacked to increase required the surface area Full pagewidth and therefore the print heads are not force. competitive due to actuator size Electro- A strong electric Low current High voltage 1989 Saito et al, static pull field is applied to consumption required U.S. Pat. No. 4,799,068 on ink the ink, whereupon Low temperature May be damaged 1989 Miura et al, electrostatic by sparks due to U.S. Pat. No. 4,810,954 attraction air breakdown Tone-jet accelerates the ink Required field towards the print strength increases medium. as the drop size decreases High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet Low power Complex IJ07, IJ10 magnet directly attracts a consumption fabrication electro- permanent magnet, Many ink types Permanent magnetic displacing ink and can be used magnetic material causing drop Fast operation such as ejection. Rare High efficiency Neodymium Iron earth magnets with Easy extension Boron (NdFeB) a field strength from single required. around 1 Tesla can nozzles to High local currents be used. Examples pagewidth print required are: Samarium heads Copper Cobalt (SaCo) and metalization magnetic materials should be used for in the neodymium long iron boron family electromigration (NdFeB, lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmented inks are usually infeasible Operating temperature limited to the Curie temperature (around 540 K) Soft A solenoid Low power Complex IJ01, IJ05, IJ08, magnetic induced a consumption fabrication IJ10, IJ12, IJ14, core magnetic field in a Many ink types Materials not IJ15, IJ17 electro- soft magnetic core can be used usually present in magnetic or yoke fabricated Fast operation a CMOS fab such from a ferrous High efficiency as NiFe, CoNiFe, material such as Easy extension or CoFe are electroplated iron from single required alloys such as nozzles to High local currents CoNiFe [1], CoFe, pagewidth print required or NiFe alloys. heads Copper Typically, the soft metalization magnetic material should be used for is in two parts, long which are electromigration normally held lifetime and low apart by a spring. resistivity When the solenoid Electroplating is is actuated, the two required parts attract, High saturation displacing the ink. flux density is required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force acts as a IJ06, IJ11, IJ13, force acting on a current consumption twisting motion IJ16 carrying wire in a Many ink types Typically, only a magnetic field is can be used quarter of the utilized. Fast operation solenoid length This allows the High efficiency provides force in a magnetic field to Easy extension useful direction be supplied from single High local currents externally to the nozzles to required print head, for pagewidth print Copper example with rare heads metalization earth permanent should be used for magnets. long Only the current electromigration carrying wire need lifetime and low be fabricated on resistivity the print-head, Pigmented inks are simplifying usually infeasible materials requirements. Magneto- The actuator uses Many ink types Force acts as a Fischenbeck, U.S. Pat. No. striction the giant can be used twisting motion 4,032,929 magnetostrictive Fast operation Unusual materials IJ25 effect of materials Easy extension such as Terfenol-D such as Terfenol-D from single are required (an alloy of nozzles to High local currents terbium, pagewidth print required dysprosium and heads Copper iron developed at High force is metalization the Naval available should be used for Ordnance long Laboratory, hence electromigration Ter-Fe-NOL). For lifetime and low best efficiency, the resistivity actuator should be Pre-stressing may pre-stressed to be required approx. 8 MPa. Surface Ink under positive Low power Requires Silverbrook, EP tension pressure is held in consumption supplementary 0771 658 A2 and reduction a nozzle by surface Simple force to effect drop related patent tension. The construction separation applications surface tension of No unusual Requires special the ink is reduced materials required ink surfactants below the bubble in fabrication Speed may be threshold, causing High efficiency limited by the ink to egress Easy extension surfactant from the nozzle. from single properties nozzles to pagewidth print heads Viscosity The ink viscosity Simple Requires Silverbrook, EP reduction is locally reduced construction supplmentary 0771 658 A2 and to select which No unusual force to effect drop related patent drops are to be materials required separation applications ejected. A in fabrication Requires special viscosity reduction Easy extension ink viscosity can be achieved from single properties electrothermally nozzles to High speed is with most inks, but pagewidth print difficult to achieve special inks can be heads Requires engineered for a oscillating ink 100:1 viscosity pressure reduction. A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave Can operate Complex drive 1993 Hadimioglu is generated and without a nozzle circuitry et al., EUP 550,192 focussed upon the plate Complex 1993 Elrod et al, drop ejection fabrication EUP 572,220 region. Low efficiency Poor control of drop position Poor control of drop volume Thermo- An actuator which Low power Efficient aqueous IJ03, IJ09, IJ17, elastic relies upon consumption operation requires IJ18, IJ19, IJ20, bend differential Many ink types a thermal insulator IJ21, IJ22, IJ23, actuator thermal expansion can be used on the hot side IJ24, IJ27, IJ28, upon Joule heating Simple planar Corrosion IJ29, IJ30, IJ31, is used. fabrication prevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35, IJ36, IJ37, required for each Pigmented inks IJ38, IJ39, IJ40, actuator may be infeasible, IJ41 Fast operation as pigment High efficiency particles may jam CMOS compatible the bend actuator voltages and currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a High force can be Requires special IJ09, IJ17, IJ18 thermo- very high generated material (e.g. IJ20, IJ21, IJ22, elastic coefficient of Three methods of PTFE) IJ23, IJ24, IJ27, actuator thermal expansion PTFE deposition Requires a PTFE IJ28, IJ29, IJ30, (CTE) such as are under deposition process, IJ31, IJ42, IJ43, polytetrafluorethy development: which is not yet IJ44 lene (PTFE) is chemical vapor standard in ULSI used. As high CTE deposition (CVD), fabs materials are spin coating, and PTFE deposition usually non- evaporation cannot be followed conductive, a PTFE is a with high heater fabricated candidate for low temperature from a conductive dielectric constant (above 350° C.) material is insulation in ULSI processing incorporated. A 50 Very low power Pigmented inks μm long PTFE consumption may be infeasable, bend actuator with Many ink types as pigment polysilicon heater can be used particles may jam and 15 mW power Simple planar the bend actuator input can provide fabrication 180 μN force and Small chip area 10 μm deflection. required for each Actuator motions actuator include: Fast operation Bend High efficiency Push CMOS compatible Buckle voltages and Rotate currents Easy extension from single nozzles to pagewidth print heads Conduct- A polymer with a High force can be Requires special IJ24 ive high coefficient of generated materials polymer thermal expansion Very low power development thermo- (such as PTFE) is consumption (High CTE elastic doped with Many ink types conductive actuator conducting can be used polymer) substances to Simple planar Requires a PTFE increase its fabrication deposition process, conductivity to Small chip area which is not yet about 3 orders of required for each standard in ULSI magnitude below actuator fabs that of copper. The Fast operation PTFE deposition conducting High efficiency cannot be followed polymer expands CMOS compatible with high when resistively voltages and temperature heated. currents (above 350° C.) Examples of Easy extension processing conducting from single Evaporation and dopants include: nozzles to CVD deposition Carbon nanotubes pagewidth print techniques cannot Metal fibers heads be used Conductive Pigmented inks polymers such as may be infeasible, doped as pigment polythiophene particles may jam Carbon granules the bend actuator Shape A shape memory High force is Fatigue limits IJ26 memory alloy such a TiNi available (stresses maximum number alloy (alos known as of hundreds of of cycles Nitinol - Nickel MPa) Low strain (1%) is Titanium alloy Large strain is required to extend developed at the available (more fatigue resistance Naval Ordnance than 3%) Cycle rate limited Laboratory) is High corrosion by heat removal thermally switched resistance Requires unusual between its weak Simple materials (TiNi) martensitic state construction The latent heat of and its high Easy extension transformation stiffness austenic from single must be provided state. The shape of nozzles to High current the actuator in its pagewidth print operation martensitic state is heads Requires pre- deformed relative Low voltage stressing to distort to the austenic operation the martensitic shape. The shape state change causes ejection of a drop. Linear Linear magnetic Linear Magnetic Requires unusual IJ12 Magnetic actuators include actuators can be semiconductor Actuator the Linear constructed with materials such as Induction Actuator high thrust, long soft magnetic (LIA), Linear travel, and high alloys (e.g. Permanent Magnet efficiency using CoNiFe) Synchronous planar Some varieties Actuator semiconductor also require (LPMSA), Linear fabrication permanent Reluctance techniques magnetic materials Synchronous Long actuator such as Actuator (LRSA), travel is available Neodymium iron Linear Switched Medium force is boron (NdFeB) Reluctance available Requires complex Actuator (LSRA), Low voltage multi-phase drive and the Linear operation circuitry Stepper Actuator High current (LSA). operation

Basic operation mode Description Advantages Disadvantages Examples Actuator This is the Simple operation Drop repetition Thermal ink jet directly simplest mode of No external fields rate is usually Piezoelectric ink pushes ink operation: the required limited to around jet actuator directly Satellite drops can 10 kHz. However, IJ01, IJ02, IJ03, supplies sufficient be avoided if drop this is not IJ04, IJ05, IJ06, kinetic energy to velocity is less fundamental to the IJ07, IJ09, IJ11, expel the drop. than 4 m/s method, but is IJ12, IJ14, IJ16, The drop must Can be efficient, related to the refill IJ20, IJ22, IJ23, have a sufficient depending upon method normally IJ24, IJ25, IJ26, velocity to the actuator used used IJ27, IJ28, IJ29, overcome the All of the drop IJ30, IJ31, IJ32, surface tension. kinetic energy IJ33, IJ34, IJ35, must be provided IJ36, IJ37, IJ38, by the actuator IJ39, IJ40, IJ41, Satellite drops IJ42, IJ43, IJ44 usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be Very simple print Requires close Silverbrook, EP printed are head fabrication proximity between 0771 658 A2 and selected by some can be used the print head and related patent manner (e.g. The drop selection the print media or applications thermally induced means does not transfer roller surface tension need to provide the May require two reduction of energy required to print heads pressurized ink). separate the drop printing alternate Selected drops are from the nozzle rows of the image separated from the Monolithic color ink in the nozzle print heads are by contact with the difficult print medium or a transfer roller. Electro- The drops to be Very simple print Requires very high Silverbrook, EP static pull printed are head fabrication electrostatic field 0771 658 A2 and on ink selected by some can be used Electrostatic field related patent manner (e.g. The drop selection for small nozzle applications thermally induced means does not sizes is above air Tone-Jet surface tension need to provide the breakdown reduction of energy required to Electrostatic field pressurized ink). separate the drop may attract dust Selected drops are from the nozzle separated from the ink in the nozzle by a strong electric field. Magnetic The drops to be Very simple print Requires magnetic Silverbrook, EP pull on ink printed are head fabrication ink 0771 658 A2 and selected by some can be used Ink colors other related patent manner (e.g. The drop selection than black are applications thermally induced means does not difficult surface tension need to provide the Requires very high reduction of energy required to magnetic fields pressurized ink). separate the drop Selected drops are from the nozzle separated from the ink in the nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator High speed (>50 Moving parts are IJ13, IJ17, IJ21 moves a shutter to kHz) operation can required block ink flow to be achieved due to Requires ink the nozzle. The ink reduced refill time pressure modulator pressure is pulsed Drop timing can Friction and wear at a multiple of the be very accurate must be considered drop ejection The actuator Stiction is possible frequency. energy can be very low Shuttered The actuator Actuators with Moving parts are IJ08, IJ15, IJ18, grill moves a shutter to small travel can be required IJ19 block ink flow used Requires ink through a grill to Actuators with pressure modulator the nozzle. The small force can be Friction and wear shutter movement used must be considered need only be equal High speed (>50 Stiction is possible to the width of the kHz) operation can grill holes. be achieved Pulsed A pulsed magnetic Extremely low Requires an IJ10 magnetic field attracts an energy operation is external pulsed pull on ink ‘ink pusher’ at the possible magnetic field pusher drop ejection No heat dissipation Requires special frequency. An problems materials for both actuator controls a the actuator and catch, which the ink pusher prevents the ink Complex pusher from construction moving when a drop is not to be ejected.

Description Advantages Disadvantages Examples Auxiliary mechanism (applied to all nozzles) None The actuator Simplicity of Drop ejection Most ink jets, directly fires the construction energy must be including ink drop, and there Simplicity of supplied by piezoelectric and is no external field operation individual nozzle thermal bubble. or other Small physical size actuator IJ01, IJ02, IJ03, mechanism IJ04, IJ05, IJ07, required. IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure Oscillating ink Requires external Silverbrook, EP ink oscillates, pressure can ink pressure 0771 658 A2 and pressure providing much of provide a refill oscillator related patent (including the drop ejection pulse, allowing Ink pressure phase applications acoustic energy. The higher operating and amplitude IJ08, IJ13, IJ15, stimul- actuator selects speed must be carefully IJ17, IJ18, IJ19, ation) which drops are to The actuators may controlled IJ21 be fired by operate with much Acoustic selectively lower energy reflections in the blocking or Acoustic lenses ink chamber must enabling nozzles. can be used to be designed for The ink pressure focus the sound on oscillation may be the nozzles achieved by vibrating the print head, or preferably by an actuator in the ink supply. Media The print head is Low power Precision assembly Silverbrook, EP proximity placed in close High accuracy required 0771 658 A2 and proximity to the Simple print head Paper fibers may related patent print medium. construction cause problems applications Selected drops Cannot print on protrude from the rough substrates print head further than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer Drops are printed High accuracy Bulky Silverbrook, EP roller to a transfer roller Wide range of Expensive 0771 658 A2 and instead of straight print substrates can Complex related patent to the print be used construction applications medium. A Ink can be dried on Tektronix hot melt transfer roller can the transfer roller piezoelectric ink also be used for jet proximity drop Any of the IJ separation. series Electro- An electric field is Low power Field strength Silverbrook, EP static used to accelerate Simple print head required for 0771 658 A2 and selected drops construction separation of small related patent towards the print drops is near or applications medium. above air Tone-Jet breakdown Direct A magnetic field is Low power Requires magnetic Silverbrook, EP magnetic used to accelerate Simple print head ink 0771 658 A2 and field selected drops of construction Requires strong related patent magnetic ink magnetic field applications towards the print medium. Cross The print head is Does not require Requires external IJ06, IJ16 magnetic placed in a magnetic materials magnet field constant magnetic to be integrated in Current densities field. The Lorenz the print head may be high, force in a current manufacturing resulting in carrying wire is process electromigration used to move the problems actuator. Pulsed A pulsed magnetic Very low power Complex print IJ10 magnetic field is used to operation is head construction field cyclically attract a possible Magnetic materials paddle, which Small print head required in print pushes on the ink. size head A small actuator moves a catch, which selectively prevents the paddle from moving.

Actuator amplification or modification method Description Advantages Disadvantages Examples None No actuator Operational Many actuator Thermal Bubble mechanical simplicity mechanisms have Ink jet Amplification is insufficient travel, IJ01, IJ02, IJ06 used. The actuator or insufficient IJ07, IJ16, IJ25, directly drives the force, to efficiently IJ26 drop ejection drive the drop process. ejection process Differential An actuator Provides greater High stresses are Piezoelectric expansion material expands travel in a reduced involved IJ03, IJ09, IJ17, bend more on one side print head area Care must be taken IJ18, IJ19, IJ20, actuator than on the other. that the materials IJ21, IJ22, IJ23, The expansion do not delaminate IJ24, IJ27, IJ29, may be thermal, Residual bend IJ30, IJ31, IJ32, piezoelectric, resulting from high IJ33, IJ34, IJ35, magnetostrictive, temperature or IJ36, IJ37, IJ38, or other high stress during IJ39, IJ42, IJ43, mechanism. The formation IJ44 bend actuator converts a high force low travel actuator mechanism to high travel, lower force mechanism. Transient A trilayer bend Very good High stresses are IJ40, IJ41 bend actuator where the temperature involved actuator two outside layers stability Care must be taken are identical. This High speed, as a that the materials cancels bend due new drop can be do not delaminate to ambient fired before heat temperature and dissipates residual stress. The Cancels residual actuator only stress of formation responds to transient heating of one side or the other. Reverse The actuator loads Better coupling to Fabrication IJ05, IJ11 spring a spring. When the the ink complexity actuator is turned High stress in the off, the spring spring releases. This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator A series of thin Increased travel Increased Some piezoelectric stack actuators are Reduced drive fabrication ink jets stacked. This can voltage complexity IJ04 be appropriate Increased where actuators possibility of short require high circuits due to electric field pinholes strength, such as electrostatic and piezoelectric actuators. Multiple Multiple smaller Increases the force Actuator forces IJ12, IJ13, IJ18, actuators actuators are used available from an may not add IJ20, IJ22, IJ28, simultaneously to actuator linearly, reducing IJ42, IJ43 move the ink. Each Multiple actuators efficiency actuator need can be positioned provide only a to control ink flow portion of the accurately force required. Linear A linear spring is Matches low travel Requires print IJ15 Spring used to transform a actuator with head area for the motion with small higher travel spring travel and high requirements force into a longer Non-contact travel, lower force method of motion motion. transformation Coiled A bend actuator is Increases travel Generally IJ17, IJ21, IJ34, actuator coiled to provide Reduces chip area restricted to planar IJ35 greater travel in a Planar implementations reduced chip area. implementations due to extreme are relatively easy fabrication to fabricate. difficulty in other orientations. Flexure A bend actuator Simple means of Care must be taken IJ10, IJ19, IJ33 bend has a small region increasing travel of not to exceed the actuator near the fixture a bend actuator elastic limit in the point, which flexes flexure area much more readily Stress distribution than the remainder is very uneven of the actuator. Difficult to The actuator accurately model flexing is with finite element effectively analysis converted from an even coiling to an angular bend, resulting in greater travel of the actuator tip. Catch The actuator Very low actuator Complex IJ10 controls a small energy construction catch. The catch Very small Requires external either enables or actuator size force disables movement Unsuitable for of an ink pusher pigmented inks that is controlled in a bulk manner. Gears Gears can be used Low force, low Moving parts are IJ13 to increase travel travel actuators required at the expense of can be used Several actuator duration. Circular Can be fabricated cycles are required gears, rack and using standard More complex pinion, ratchets, surface MEMS drive electronics and other gearing processes Complex methods can be construction used. Friction, friction, and wear are possible Buckle A buckle plate can Very fast Must stay within S. Hirata et al, “An plate be used to change movement elastic limits of the Ink-jet Head Using a slow actuator achievable materials for long Diaphragm into a fast motion. device life Microactuator”, It can also convert High stresses Proc. IEEE a high force, low involved MEMS, Feb. 1996, travel actuator into Generally high pp 418-423. a high travel, power requirement IJ18, IJ27 medium force motion. Tapered A tapered Linearizes the Complex IJ14 magnetic magnetic pole can magnetic construction pole increase travel at force/distance the expense of curve force. Lever A lever and Matches low travel High stress around IJ32, IJ36, IJ37 fulcrum is used to actuator with the fulcrum transform a motion higher travel with small travel requirements and high force into Fulcrum area has a motion with no linear longer travel and movement, and lower force. The can be used for a lever can also fluid seal reverse the direction of travel. Rotary The actuator is High mechanical Complex IJ28 impeller connected to a advantage construction rotary impeller. A The ratio of force Unsuitable for small angular to travel of the pigmented inks deflection of the actuator can be actuator results in matched to the a rotation of the nozzle impeller vanes, requirements by which push the ink varying the against stationary number of impeller vanes and out of vanes the nozzle. Acoustic A refractive or No moving parts Large area 1993 Hadimioglu lens diffractive (e.g. required et al, EUP 550,192 zone plate) Only relevant for 1993 Elrod et al, acoustic lens is acoustic ink jets EUP 572,220 used to concentrate sound waves. Sharp A sharp point is Simple Difficult to Tone-jet conductive used to concentrate construction fabricate using point an electrostatic standard VLSI field. processes for a surface ejecting ink-jet Only relevant for electrostatic ink jets

Actuator motion Description Advantages Disadvantages Examples Volume The volume of the Simple High energy is Hewlett-Packard expansion actuator changes, construction in the typically required Thermal Ink jet pushing the ink in case of thermal ink to achieve volume Canon Bubblejet all directions. jet expansion. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, The actuator Efficient coupling High fabrication IJ01, IJ02, IJ04, normal to moves in a to ink drops complexity may be IJ07, IJ11, IJ14 chip direction normal to ejected normal to required to achieve surface the print head the surface perpendicular surface. The motion nozzle is typically in the line of movement. Parallel to The actuator Suitable for planar Fabrication IJ12, IJ13, IJ15, chip moves parallel to fabrication complexity IJ33, , IJ34, IJ35, surface the print head Friction IJ36 surface. Drop Stiction ejection may still be normal to the surface. Membrane An actuator with a The effective area Fabrication 1982 Howkins push high force but of the actuator complexity U.S. Pat. No. 4,459,601 small area is used becomes the Actuator size to push a stiff membrane area Difficulty of membrane that is integration in a in contact with the VLSI process ink. Rotary The actuator Rotary levers may Device complexity IJ05, IJ08, IJ13, causes the rotation be used to increase May have friction IJ28 of some element, travel at a pivot point such a grill or Small chip area impeller requirements Bend The actuator bends A very small Requires the 1970 Kyser et al when energized. change in actuator to be U.S. Pat. No. 3,946,398 This may be due to dimensions can be made from at least 1973 Stemme U.S. Pat. No. differential converted to a two distinct layers, 3,747,120 thermal expansion, large motion. or to have a IJ03, IJ09, IJ10, piezoelectric thermal difference IJ19, IJ23, IJ24, expansion, across the actuator IJ25, IJ29, IJ30, magnetostriction, IJ31, IJ33, IJ34, or other form of IJ35 relative dimensional change. Swivel The actuator Allows operation Inefficient IJ06 swivels around a where the net coupling to the ink central pivot. This linear force on the motion motion is suitable paddle is zero where there are Small chip area opposite forces requirements applied to opposite sides of the paddle, e.g. Lorenz force. Straighten The actuator is Can be used with Requires careful IJ26, IJ32 normally bent, and shape memory balance of stresses straightens when alloys where the to ensure that the energized. austenic phase is quiescent bend is planar accurate Double The actuator bends One actuator can Difficult to make IJ36, IJ37, IJ38 bend in one direction be used to power the drops ejected when one element two nozzles. by both bend is energized, and Reduced chip size. directions bends the other Not sensitive to identical. way when another ambient A small efficiency element is temperature loss compared to energized. equivalent single bend actuators. Shear Energizing the Can increase the Not readily 1985 Fishbeck actuator causes a effective travel of applicable to other U.S. Pat. No. 4,584,590 shear motion in the piezoelectric actuator actuator material. actuators mechanisms Radial The actuator Relatively easy to High force 1970 Zoltan U.S. Pat. No. con- squeezes an ink fabricate single required 3,683,212 striction reservoir, forcing nozzles from glass Inefficient ink from a tubing as Difficult to constricted nozzle. macroscopic integrate with structures VLSI processes Coil/ A coiled actuator Easy to fabricate Difficult to IJ17, IJ21, IJ34, uncoil uncoils or coils as a planar VLSI fabricate for non- IJ35 more tightly. The process planar devices motion of the free Small area Poor out-of-plane end of the actuator required, therefore stiffness ejects the ink. low cost Bow The actuator bows Can increase the Maximum travel is IJ16, IJ18, IJ27 (or buckles) in the speed of travel constrained middle when Mechanically rigid High force energized. required Push-Pull Two actuators The structure is Not readily IJ18 control a shutter. pinned at both suitable for ink jets One actuator pulls ends, so has a high which directly the shutter, and the out-of-plane push the ink other pushes it. rigidity Curl A set of actuators Good fluid flow to Design complexity IJ20, IJ42 inwards curl inwards to the region behind reduce the volume the actuator of ink that they increases enclose. efficiency Curl A set of actuators Relatively simple Relatively large IJ43 outwards curl outwards, construction chip area pressurizing ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes High efficiency High fabrication IJ22 enclose a volume Small chip area complexity of ink. These Not suitable for simultaneously pigmented inks rotate, reducing the volume between the vanes. Acoustic The actuator The actuator can Large area 1993 Hadimioglu vibration vibrates at a high be physically required for et al, EUP 550,192 frequency. distant from the efficient operation 1993 Elrod et al, ink at useful EUP 572,220 frequencies Acoustic coupling and crosstalk Complex drive circuitry Poor control of drop volume and position None In various ink jet No moving parts Various other Silverbrook, EP designs the tradeoffs are 0771 658 A2 and actuator does not required to related patent move. eliminate moving applications parts Tone-jet

Nozzle refill method Description Advantages Disadvantages Examples Surface This is the normal Fabrication Low speed Thermal ink jet tension way that ink jets simplicity Surface tension Piezoelectric ink are refilled. After Operational force relatively jet the actuator is simplicity small compared to IJ01-IJ07, IJ10- energized, it actuator force IJ14, IJ16, IJ20, typically returns Long refill time IJ22-IJ45 rapidly to its usually dominates normal position. the total repetition This rapid return rate sucks in air through the nozzle opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle High speed Requires common IJ08, IJ13, IJ15, oscillating chamber is Low actuator ink pressure IJ17, IJ18, IJ19, ink provided at a energy, as the oscillator IJ21 pressure pressure that actuator need only May not be oscillates at twice open or close the suitable for the drop ejection shutter, instead of pigmented inks frequency. When a ejecting the ink drop is to be drop ejected, the shutter is opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill After the main High speed, as the Requires two IJ09 actuator actuator has nozzle is actively independent ejected a drop a refilled actuators per second (refill) nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive The ink is held a High refill rate, Surface spill must Silverbrook, EP ink slight positive therefore a high be prevented 0771 658 A2 and pressure pressure. After the drop repetition rate Highly related patent ink drop is ejected, is possible hydrophobic print applications the nozzle head surfaces are Alternative for:, chamber fills required IJ01-IJ07, IJ10- quickly as surface IJ14, IJ16, IJ20, tension and ink IJ22-IJ45 pressure both operate to refill the nozzle.

Method of restricting back-flow through inlet Description Advantages Disadvantages Examples Long inlet The ink inlet Design simplicity Restricts refill rate Thermal ink jet channel channel to the Operational May result in a Piezoelectric ink nozzle chamber is simplicity relatively large jet made long and Reduces crosstalk chip area IJ42, IJ43 relatively narrow, Only partially relying on viscous effective drag to reduce inlet back-flow. Positive The ink is under a Drop selection and Requires a method Silverbrook, EP ink positive pressure, separation forces (such as a nozzle 0771 658 A2 and pressure so that in the can be reduced rim or effective related patent quiescent state Fast refill time hydrophobizing, or applications some of the ink both) to prevent Possible operation drop already flooding of the of the following: protrudes from the ejection surface of IJ01-IJ07, IJ09- nozzle. the print head. IJ12, IJ14, IJ16, This reduces the IJ20, IJ22, , IJ23- pressure in the IJ34, IJ36-IJ41, nozzle chamber IJ44 which is required to eject a certain volume of ink. The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more The refill rate is Design complexity HP Thermal Ink baffles are placed not as restricted as May increase Jet in the inlet ink the long inlet fabrication Tektronix flow. When the method. complexity (e.g. piezoelectric ink actuator is Reduces crosstalk Tektronix hot melt jet energized, the Piezoelectric print rapid ink heads). movement creates eddies which restrict the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible In this method Significantly Not applicable to Canon flap recently disclosed reduces back-flow most ink jet restricts by Canon, the for edge-shooter configurations inlet expanding actuator thermal ink jet Increased (bubble) pushes on devices fabrication a flexible flap that complexity restricts the inlet. Inelastic deformation of polymer flap results in creep over extended use Inlet filter A filter is located Additional Restricts refill rate IJ04, IJ12, IJ24, between the ink advantage of ink May result in IJ27, IJ29, IJ30 inlet and the filtration complex nozzle chamber. Ink filter may be construction The filter has a fabricated with no multitude of small additional process holes or slots, steps restricting ink flow. The filter also removes particles which may block the nozzle. Small inlet The ink inlet Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared channel to the May result in a to nozzle nozzle chamber relatively large has a substantially chip area smaller cross Only partially section than that of effective the nozzle, resulting in easier ink egress out of the nozzle than out of the inlet. Inlet A secondary Increases speed of Requires separate IJ09 shutter actuator controls the ink-jet print refill actuator and the position of a head operation drive circuit shutter, closing off the ink inlet when the main actuator is energized. The inlet The method avoids Back-flow Requires careful IJ01, IJ03, IJ05, is located the problem of problem is design to minimize IJ06, IJ07, IJ10, behind the inlet back-flow by eliminated the negative IJ11, IJ14, IJ16, ink- arranging the ink- pressure behind IJ22, IJ23, IJ25, pushing pushing surface of the paddle IJ28, IJ31, IJ32, surface the actuator IJ33, IJ34, IJ35, between the inlet IJ36, IJ39, IJ40, and the nozzle. IJ41 Part of the The actuator and a Significant Small increase in IJ07, IJ20, IJ26, actuator wall of the ink reductions in back- fabrication IJ38 moves to chamber are flow can be complexity shut off arranged so that achieved the inlet the motion of the Compact designs actuator closes off possible the inlet. Nozzle In some Ink back-flow None related to ink Silverbrook, EP actuator configurations of problem is back-flow on 0771 658 A2 and does not ink jet, there is no eliminated actuation related patent result in expansion or applications ink back- movement of an Valve-jet flow actuator which Tone-jet may cause ink back-flow through the inlet.

Nozzle Clearing Method Description Advantages Disadvantages Examples Normal nozzle All of the nozzles are fired No added complexity on the May not be sufficient to Most ink jet systems firing periodically, before the ink has print head displace dried ink IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, a chance to dry. When not in IJ07, IJ09, IJ10, IJ11, IJ12, IJ14, used the nozzles are sealed IJ16, IJ20, IJ22, IJ23, IJ24, IJ25, (capped) against air. The nozzle IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, firing is usually performed IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, during a special clearing IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, cycle, after first moving the IJ45 print head to a cleaning station. Extra power In systems which heat the ink, Can be highly effective if the Requires higher drive voltage Silverbrook, EP 0771 658 A2 to ink heater but do not boil it under normal heater is adjacent to the nozzle for clearing and related patent applications situations, nozzle clearing can be May require larger drive achieved by over-powering the transistors heater and boiling ink at the nozzle. Rapid success- The actuator is fired in rapid Does not require extra drive Effectiveness depends sub- May be used with: IJ01, IJ02, ion of actuator succession. In some configura- circuits on the print head stantially upon the configuration IJ03, IJ04, IJ05, IJ06, IJ07, IJ09, pulses tions, this may cause heat build- Can be readily controlled and of the ink jet nozzle IJ10, IJ11, IJ14, IJ16, IJ20, IJ22, up at the nozzle which boils the initiated by digital logic IJ23, IJ24, IJ25, IJ27, IJ28, IJ29, ink, clearing the nozzle. In other IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, situations, it may cause IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, sufficient vibrations to dislodge IJ43, IJ44, IJ45 clogged nozzles. Extra power Where an actuator is not A simple solution where Not suitable where there is a May be used with: IJ03, IJ09, to ink pushing normally driven to the limit of applicable hard limit to actuator IJ16, IJ20, IJ23, IJ24, IJ25, IJ27, actuator its motion, nozzle clearing may movement IJ29, IJ30, IJ31, IJ32, IJ39, IJ40, be assisted by providing an IJ41, IJ42, IJ43, IJ44, IJ45 enhanced drive signal to the actuator. Acoustic An ultrasonic wave is applied A high nozzle clearing capability High implementation cost if IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, resonance to the ink chamber. This wave can be achieved system does not already include IJ21 is of an appropriate amplitude May be implemented at very low an acoustic actuator and frequency to cause sufficient cost in systems which already force at the nozzle to clear include acoustic actuators blockages. This is easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle clearing A microfabricated plate is Can clear severely clogged Accurate mechanical alignment Silverbrook, EP 0771 658 A2 plate pushed against the nozzles. nozzles is required and related patent applications The plate has a post for every Moving parts are required nozzle. A post moves through There is risk of damage to each nozzle, displacing dried the nozzles ink. Accurate fabrication is required Ink pressure The pressure of the ink is May be effective where other Requires pressure pump or other May be used with all IJ series pulse temporarily increased so that methods cannot be used pressure actuator ink jets ink streams from all of the Expensive nozzles. This may be used in Wasteful of ink conjunction with actuator energizing. Print head A flexible ‘blade’ is wiped Effective for planar print Difficult to use if print head Many ink jet systems wiper across the print head surface. head surfaces surface is non-planar or very The blade is usually fabricated Low cost fragile from a flexible polymer, e.g. Requires mechanical parts rubber or synthetic elastomer. Blade can wear out in high volume print systems Separate ink A separate heater is provided Can be effective where other Fabrication complexity Can be used with many IJ series boiling heater at the nozzle although the nozzle clearing methods cannot ink jets normal drop e-ection mechanism be used does not require it. The heaters Can be implemented at no do not require individual drive additional cost in some ink circuits, as many nozzles can be jet configurations cleared simultaneously, and no imaging is required.

Nozzle plate construction Description Advantages Disadvantages Examples Electroformed A nozzle plate is separately Fabrication simplicity High temperatures and pressures Hewlett Packard Thermal Ink jet nickel fabricated from electroformed are required to bond nozzle nickel, and bonded to the plate print head chip. Minimum thickness constraints Differential thermal expansion Laser ablated Individual nozzle holes are No masks required Each hole must be individually Canon Bubblejet 1988 Sercel et or drilled ablated by an intense UV laser Can be quite fast formed al., SPIE, Vol. 998 Excimer polymer in a nozzle plate, which is Some control over nozzle Special equipment required Beam Applications, pp. 76-83 typically a polymer such as profile is possible Slow where there are many 1993 Watanabe et al., U.S. Pat. polyimide or polysulphone Equipment required is relatively thousands of nozzles per No. 5,208,604 low cost print head May produce thin burrs at exit holes Silicon micro- A separate nozzle plate is High accuracy is attainable Two part construction K. Bean, IEEE Transactions on machined micromachined from single High cost Electron Devices, Vol. ED-25, crystal silicon, and bonded to Requires precision alignment No. 10, 1978, pp 1185-1195 the print head wafer. Nozzles may be clogged by Xerox 1990 Hawkins et al., U.S. adhesive Pat. No. 4,899,181 Glass Fine glass capillaries are drawn No expensive equipment Very small nozzle sizes are 1970 Zoltan U.S. Pat. No. capillaries from glass tubing. This method required difficult to form 3,683,212 has been used for making Simple to make single nozzles Not suited for mass individual nozzles, but is production difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is deposited as High accuracy (<1 μm) Requires sacrificial layer Silverbrook, EP 0771 658 A2 surface micro- a layer using standard VLSI Monolithic under the nozzle plate to form and related patent applications machined using deposition techniques. Nozzles Low cost the nozzle chamber IJ01, IJ02, IJ04, IJ11, IJ12, IJ17, VLSI litho- are etched in the nozzle Existing processes can be used Surface may be fragile to the IJ18, IJ20, IJ22, IJ24, IJ27, IJ28, graphic plate using VLSI lithography touch IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, processes and etching. IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a buried etch High accuracy (<1 μm) Requires long etch times IJ03, IJ05, IJ06, IJ07, IJ08, IJ09, etched through stop in the wafer. Nozzle Monolithic Requires a support wafer IJ10, IJ13, IJ14, IJ15, IJ16, IJ19, substrate chambers are etched in the Low cost IJ21, IJ23, IJ25, IJ26 front of the wafer, and the No differential expansion wafer is thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle plate Various methods have been tried No nozzles to become clogged Difficult to control drop Ricoh 1995 Sekiya et al U.S. to eliminate the nozzles entirely, position accurately Pat. No. 5,412,413 to prevent nozzle clogging. Crosstalk problems 1993 Hadimioglu et al EUP These include thermal bubble 550,192 mechanisms and acoustic lens 1993 Elrod et al EUP 572,220 mechanisms Trough Each drop ejector has a trough Reduced manufacturing Drop firing direction is IJ35 through which a paddle moves. complexity sensitive to wicking. There is no nozzle plate. Monolithic Nozzle slit The elimination of nozzle holes No nozzles to become clogged Difficult to control drop position 1989 Saito et al U.S. Pat. No. instead of and replacement by a slit Crosstalk problems 4,799,068 individual encompassing many actuator nozzles positions reduces nozzle clogging, but increases cross- talk due to ink surface waves Drop ejection direction Description Advantages Disadvantages Examples Edge (‘edge Ink flow is along the surface Simple construction Nozzles limited to edge Canon Bubblejet 1979 Endo et shooter’) of the chip, and ink drops are No silicon etching required High resolution is difficult al GB patent 2,007,162 ejected from the chip edge. Good heat sinking via substrate Fast color printing requires Xerox heater-in-pit Mechanically strong one print head per color 1990 Hawkins et al U.S. Pat. Ease of chip handing No. 4,899,181 Tone-jet Surface (‘roof Ink flow is along the surface No bulk silicon etching Maximum ink flow is severely Hewlett-Packard TIJ 1982 shooter’) of the chip, and ink drops required restricted Vaught et al U.S. Pat. No. are ejected from the chip Silicon can make an effective 4,490,728 surface, normal to the plane heat sink IJ02, IJ11, IJ12, IJ20, IJ22 of the chip. Mechanical strength Through chip, Ink flow is through the chip, High ink flow Requires bulk silicon etching Silverbrook, EP 0771 658 A2 forward (‘up and ink drops are ejected from Suitable for pagewidth and related patent applications shooter’) the front surface of the print heads IJ04, IJ17, IJ18, IJ24, IJ27-IJ45 chip. High nozzle packing density therefore low manufacturing cost

Drop ejection direction Description Advantages Disadvantages Examples Through chip, Ink flow is through the chip, High ink flow Requires wafer thinning IJ01, IJ03, IJ05, IJ06, IJ07, IJ08, reverse (‘down and ink drops are ejected from Suitable for pagewidth Requires special handling IJ09, IJ10, IJ13, IJ14, IJ15, IJ16, shooter’) the rear surface of the chip. print heads during manufacture IJ19, IJ21, IJ23, IJ25, IJ26 High nozzle packing density therefore low manufacturing cost Through Ink flow is through the actuator, Suitable for piezoelectric Pagewidth print heads require Epson Stylus actuator which is not fabricated as part print heads several thousand connections to Tektronix hot melt piezo- of the same substrate as the drive circuits electric ink jets drive transistors. Cannot be manufactured in standard CMOS fabs Complex assembly required

Ink type Description Advantages Disadvantages Examples Aqueous, dye Water based ink which typically Environmentally friendly Slow drying Most existing ink jets contains: water, dye, surfactant, No odor Corrosive All IJ series ink jets humectant, and biocide. Modern Bleeds on paper Silverbrook, EP 0771 658 A2 ink dyes have high water- May strikethrough and related patent applications fastness, light fastness Cockles paper Aqueous, pig- Water based ink which typically Environmentally friendly Slow drying IJ02, IJ04, IJ21, IJ26, IJ27, IJ30 ment contains: water, pigment, No odor Corrosive Silverbrook, EP 0771 658 A2 surfactant, humectant, and Reduced bleed Pigment may clog nozzles and related patent applications biocide. Pigments have an Reduced wicking Pigment may clog actuator Piezoelectric ink-jets advantage in reduced bleed, Reduced strikethrough mechanisms Thermal ink jets (with wicking and strikethrough. Cockles paper significant restrictions) Methyl Ethyl MEK is a highly volatile Very fast drying Odorous All IJ series ink jets Ketone (MEK) solvent used for industrial Prints on various sub- Flammable printing on difficult surfaces strates such as metals and such as aluminium cans. plastics Alcohol Alcohol based inks can be used Fast drying Slight odor All IJ series ink jets (ethanol, 2- where the printer must operate Operates at sub-freezing Flammable butanol, and at temperatures below the temperatures others) freezing point of water. An Reduced paper cockle example of this is in-camera Low cost consumer photographic printing. Phase change The ink is solid at room temper- No drying time-ink instantly High viscosity Tektronix hot melt piezo- (hot melt) ature, and is melted in the print freezes on the print medium Print ink typically has a ‘waxy’ electric ink jets head before jetting. Hot melt Almost any print medium can be feel 1989 Nowak U.S. Pat. No. inks are usually wax based, used Printed pages may ‘block’ 4,820,346 with a melting point around No paper cockle occurs Ink temperature may be above All IJ series ink jets 80° C.. After jetting the No wicking occurs the curie point of permanent ink freezes almost instantly No bleed occurs magnets upon contacting the print No strikethrough occurs Ink heaters consume power medium or a transfer roller. Long warm-up time Oil Oil based inks are extensively High solubility medium for High viscosity: this is a All IJ series ink jets used in offset printing. They some dyes significant limitation for use in have advantages in improved Does not cockle paper ink jets, which usually require characteristics on paper Does not wick through paper a low viscosity. Some short (especially no wicking or chain and multi-branched oils cockle). Oil soluble dies have a sufficiently low viscosity. and pigments are required. Slow drying Microemulsion A microemulsion is a stable, self Stops ink bleed Viscosity higher than water All IJ series ink jets forming emulsion of oil, water, High dye solubility Cost is slightly higher than and surfactant. The characteristic Water, oil, and amphiphilic water based ink drop size is less than 100 nm, soluble dies can be used High surfactant concentra- and is determined by the Can stabilize pigment tion required (around 5%) preferred curvature of the suspensions surfactant. 

We claim:
 1. An ink jet printhead comprising: a nozzle chamber having an ink ejection port in one wall of said chamber; an ink supply source interconnected to said nozzle chamber via another wall of said chamber; a first moveable actuator in said another wall of said chamber for ejecting ink from said ink ejection port; and a second moveable actuator in said another wall of said chamber for pumping ink into said chamber from said ink supply source after said first actuator has caused the ejection of ink from said chamber.
 2. An ink jet printhead as claimed in claim 1 wherein said actuators comprise thermal bend actuators.
 3. An ink jet printhead as claimed in claim 1 wherein said first actuator is arranged substantially opposite said ink ejection port and first and second actuators form segments of a nozzle chamber wall opposite said ink ejection port and between said nozzle chamber and ink supply source.
 4. An ink jet printhead as claimed in claim 1 wherein said actuators comprise a conductive heater element encased within a material having a high co-efficient of thermal expansion whereby said actuators operate by means of electrical heating by said heater element.
 5. An ink jet printhead as claimed in claim 4 wherein said heater element is of a serpentine form and is concertinaed upon heating so as to allow substantially unhindered expansion of said material during heating.
 6. An ink jet printhead as claimed in claim 4 wherein said actuator material has a high coefficient of thermal expansion and comprises substantially polytetrafluoroethylene.
 7. An ink jet printhead as claimed in claim 4 wherein said heater material comprises substantially copper.
 8. An ink jet printhead as claimed in claim 2 wherein the thermal actuators are attached to a substrate and the heating of said actuators is primarily near the attached end of said device.
 9. An ink jet printhead as claimed in claim 1, wherein: (a) said first actuator ejects ink from said ink ejection port; and (b) said second actuator pumps ink towards said ink ejection port so as to rapidly refill the nozzle chamber around the area of said ink ejection port.
 10. An ink jet printhead as claimed in claim 1 wherein surfaces of said actuators are treated to make them hydrophilic.
 11. An ink jet printhead as claimed in claim 1 wherein said actuators are formed by utilization of a sacrificial material layer which is etched away to release said actuators.
 12. An ink jet printhead as claimed in claim 1 wherein portions of said nozzle include a silicon nitride covering so as to insulate and passivate them from adjacent portions.
 13. An ink jet printhead as claimed in claim 1 wherein said nozzle chamber is formed from crystallographic etching of a silicon substrate.
 14. An ink jet printhead as claimed in claim 1 wherein said nozzle is constructed via fabrication from a silicon wafer utilizing semiconductor fabrication techniques.
 15. An ink jet printhead as claimed in any one of claims 1 to 5 wherein: (a) said first actuator is activated to eject ink from said ink ejection port; (b) said first actuator is deactivated so as to cause a portion of said ejected ink to break off from a main body of ink within said nozzle chamber; (c) said second actuator is activated to pump ink towards said ink ejection port so as to rapidly refill the nozzle chamber around the are of said ink ejection port; and (d) said first actuator is activated to eject ink from the ink ejection port while simultaneously deactivating said second actuator so as to return to its quiescent position; otherwise (e) said second actuator is deactivated to return to its quiescent position.
 16. An ink jet printhead comprising: a nozzle chamber having an ink ejection port in one wall of said chamber; an ink supply source interconnected to said nozzle chamber via another wall of said chamber; a first moveable actuator in said another wall of said chamber for ejecting ink from said ink ejection port said first moveable actuator being arranged substantially opposite said ink ejection port; a second moveable actuator in said another wall of said chamber for pumping ink into said chamber from said ink supply source after said first actuator has caused the ejection of ink from said chamber, wherein said first and second actuators form segments of a nozzle chamber wall opposite said ink ejection port and between said nozzle chamber and ink supply source; and said actuators comprise a conductive heater element encased within a material having a high co-efficient of thermal expansion whereby said actuators operate by means of electrical heating by said heater element and wherein said heater element is of a serpentine form and is concertinaed upon heating so as to allow substantially unhindered expansion of said material during heating. 